Light scanning device

ABSTRACT

A light scanning device, including a light source including plural light emitting elements arranged linearly, a deflection section that deflects plural light beams emitted from the light source to scan a surface to be scanned, a photosensor that receives at least one of the plural light beams that are deflected by the deflection section, a signal generation section that generates a signal when a light energy amount received at the photosensor reaches a predetermined amount, and a control section that starts scanning of the surface to be scanned by each light beam after a predetermined amount of time passes from a point in time when the signal is generated by the signal generation section, the light receiving surface of the photosensor being inclined to receive light beams emitted from at least two light emitting elements among the plural light emitting elements, is provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese PatentApplication No. 2005-216541, the disclosure of which is incorporated byreference herein.

BACKGROUND

1. Technical Field

The present invention relates to a light scanning device for scanning asurface to be scanned by deflecting plural light beams emitted from alight source by a deflection section.

2. Related Art

In an image forming device in an electronographic system, for highresolution and high speed, a light scanning device has been widely used,which simultaneously emits plural light beams from a light source inwhich plural light emitting elements such as a semiconductor laser isarranged two-dimensionally and deflects them on the same deflectionsurface to scan a photoreceptor at the same time by plural light beamssimultaneously. In addition, as a light source of this light scanningdevice, a Vertical Cavity Surface Emitting Laser (a so-called VCSEL) hasbeen widely used because of its high degree of freedom in arrangement ofthe semiconductor laser and low manufacturing cost.

In the light scanning device, generally, a photodetector is arranged sothat light beam at starting of a main scanning can enter upon. Thisphotodetector generates a scanning onset signal (hereinafter, called asa SOS signal) in accordance with timing of detection of the scanned beamand a driving circuit of a light source controls a start position of themain scanning based on a SOS signal generated by the photodetector.

As shown in FIG. 9, as a photodetector, one configured by a photodiodeapplying a current depending on a light incident amount, an amplifier OPfor perform I (current)/V (voltage) conversion by amplifying theinputted current, a threshold power source SP for generating a voltageindicating a threshold, and a comparator CP for comparing each outputvoltage of the amplifier OP and the threshold power source SP has beenwidely known. In this photodetector, the SOS signal is made a high levelwhen the output voltage of an amplifier OP is not less than a threshold.

It is general that a single mode oscillation (oscillation in a singlewave length) is required for the light scanning device in order toobtain a minute beam spot, however, if the single mode oscillation ismade in the VCSEL, there is a tendency that the light emission output issmall. Therefore, in the case of scanning a photodiode PD by lightingonly one VCSEL, the light energy amount received by the photodiode PD issmall. So it may be required that the amplification gain of thephotodiode PD is increased or the threshold voltage is decreased.However, in this case, this makes the scanning easily affected by thenoise. Therefore, a method to increase a light energy amount received bythe photodiode PD by lighting plural VCSELs of which positions in themain scanning directions are close to each other and scanning thephotodiode PD is devised.

According to this method, when there is no displacement in the positionsin the main scanning directions of plural VCSELs (Δ=0 μm), plural lightbeams emitted from the plural VCSELs at the same time enters thephotodiode PD at the same time, so that, as shown in a graph of FIG. 10,a received light energy profile is formed, which has one rising and onefalling and has the maximum value larger than the light emission energyamount of each VCSEL. Therefore, there are only two cross points betweenthe received light energy profile and an energy level corresponding to athreshold vale of generation of a SOS signal without raising theamplification gain of the photodiode PD or lowering the thresholdvoltage, and this makes it possible to generate a SOS signal stably.Further, the graph of FIG. 10 shows a received light energy profile in amain scanning direction in the photodiode PD when three VCSELs havingGaussian distribution with a beam diameter of 60 μmare lighted at thesame time to scan the photodiode PD.

However, if there is a displacement in the positions of the mainscanning directions of plural VCSELs (Δ=100 μm), there is a differencein times that plural light beams emitted from the plural VCSELs at thesame time enter the photodiode PD. Therefore, as shown in the graph ofFIG. 10, rising and falling are repeated for each light beam and thereceived light energy profile of which the maximum value issubstantially equivalent to the light emission energy amount of eachVCSEL is formed. Therefore, in order to make only two cross pointsbetween the received light energy profile and the energy levelcorresponding to the threshold vale of generation of the SOS signal, theamplification gain of the photodiode PD should be increased or thethreshold voltage should be increased, and this makes the affect of thenoise easy to receive.

SUMMARY

An aspect of the invention is a light scanning device including: a lightsource including plural light emitting elements that are arrangedlinearly; a deflection section that deflects plural light beams emittedfrom the light source to scan a surface to be scanned; a photosensorthat receives at least one of the plural light beams that are deflectedby the deflection section; a signal generation section that generates asignal when an amount of light energy received at the photosensorreaches a predetermined amount; and a control section that startsscanning of the surface to be scanned by each light beam after apredetermined time passes from a point in time when the signal isgenerated by the signal generation section; wherein a light receivingsurface of the photosensor is inclined so as to receive light beamsemitted from at least two light emitting elements among the plural lightemitting elements.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will be described in detail withreference to the following figures, wherein:

FIG. 1 is a perspective view showing a light scanning device accordingto a first exemplary embodiment;

FIG. 2 is a schematic diagram explaining the operation of the lightscanning device according to the first exemplary embodiment;

FIG. 3 is a graph showing a received light energy amount profile on alight receiving surface of a photosensor of the light scanning deviceaccording to the first exemplary embodiment;

FIGS. 4A, 4B, and 4C show a sensor adjusting mechanism of thephotosensor of the light scanning device according to the firstexemplary embodiment; FIG. 4A is a front view; FIG. 4B is a side view;and FIG. 4C is a plan view;

FIG. 5 is a block diagram showing the configuration of an exposurecontrol section of the light scanning device according to the firstexemplary embodiment;

FIG. 6 is a timing chart showing the state of a substantial part signalof the exposure control section according to a second exemplaryembodiment;

FIG. 7 is a perspective view showing a light scanning device accordingto the second exemplary embodiment;

FIGS. 8A, 8B, and 8C show a sensor adjusting mechanism of a photosensorof the light scanning device according to the second exemplaryembodiment; FIG. 8A is a front view; FIG. 8B is a side view; and FIG. 8Cis a plan view;

FIG. 9 is a circuit diagram showing a circuit configuration example of aphotodetector; and

FIG. 10 is a graph showing a received light energy amount profile on alight receiving face of a conventional light scanning device.

DETAILED DESCRIPTION

With reference to the drawings, the exemplary embodiments of theinvention will be described below.

First Exemplary Embodiment

As shown in FIG. 1, a light scanning device 10 according to the firstexemplary embodiment is provided with a VCSEL array 16 having pluralVCSELs 16A arranged two-dimensionally. At the side of light emission ofthe VCSEL array 16, a collimator lens 36, a cylindrical lens 38, and apolygon mirror 40 are disposed in that order, and further, at the sideof light deflection of the polygon mirror 40, an fθ lens 44 and aphotoreceptor 46 are disposed in that order.

The laser beams emitted from the VCSEL array 16 are made to beapproximately parallel beam by the collimator lens 36. This laser beamis converged in the sub scanning direction by the cylindrical lens 38 tobe focused on a reflection surface of the polygon mirror 40. Then, it isdeflected by the rotation of the polygon mirror 40 to be imaged on thephotoreceptor 46 via the fθ lens 44. Further, the main scanning iscarried out by rotation in an arrow A direction of the polygon mirror 40and the sub scanning is carried out by rotation in an arrow B directionof the photoreceptor 46.

On the other hand, a reflection mirror 48 is provided at a positionwhere the main scanning is started by the laser beam. Further, in thereflection direction of this reflection mirror 48, a lens 49 having apositive power in the sub scanning direction and a photosensor 50configured by a photodiode are provided so that the laser beam when themain scanning is started enters the photosensor 50 passing through thelens 49. Then, in accordance with incidence of the laser beam in thephotosensor 50, a SOS signal is generated by a photodetector for a SOSsignal detection 52 (refer to FIG. 5) which will be described later.

The photodetector for SOS signal detection 52 according to thisexemplary embodiment is configured in the same way as the photodetectorshown in FIG. 9. Here, the photodiode PD shown in FIG. 9 corresponds tothe photosensor 50 of this exemplary embodiment.

In addition, the reflection surface of the polygon mirror 40 and thelight receiving surface 50A of the photosensor 50 are in a conjugaterelation. Even if optical surface tangle of the reflection surface ofthe polygon mirror 40 occurs, the incidence position of the light beamin the light receiving surface 50A of the photosensor 50 is not shiftedin the sub scanning direction.

As shown in FIG. 2, in the light scanning device 10 according to thisexemplary embodiment, the photosensor 50 is scanned in a state of aVCSEL group (hereinafter, referred to as “a SOS detection group”) beinglighted, the group emitting light beams which beam spots formed on thephotoreceptor 46 are arranged linearly, and then, the SOS signal isgenerated in accordance with the output from the photosensor 50depending on the scanning.

As shown in FIG. 1 and FIG. 2, the plural VCSELs 16A (for example, threeas shown in FIG. 2) configuring the SOS detection group are arranged ona line inclined toward a side of the downstream of the main scanningdirection (a direction parallel to a surface(s) at which each membersare disposed shown in FIG. 1) with respect to the sub scanning direction(a direction perpendicular to the surface(s) at which each members aredisposed shown in FIG. 1). The photoreceptor 46 is scanned by row of thelight beams inclined to the downstream of the main scanning directionwith respect to the sub scanning direction. On the other hand, the lightreceiving surface 50A of the photosensor 50 is scanned by row of thelight beams inclined toward the upstream of the scanning direction inthe light receiving surface 50A with respect to the sub scanningdirection. Further, since the light beams are reflected by thereflection mirror 48 to enter the light receiving surface 50A of thephotosensor 50, in the photoreceptor 46 and the light receiving surface50A of the photosensor 50, the scanning directions thereof are invertedand the inclined directions thereof with respect to the sub scanningdirection of the row of the light beams to be scanned are inverted.

Here, as shown in FIG. 2, the light receiving surface 50A of thephotosensor 50 is formed in the shape of a rectangle in which adirection inclined toward the side of the upstream in the scanningdirection on the light receiving surface 50A with respect to the subscanning direction is a longitudinal direction. In addition, thelongitudinal direction of the light receiving surface 50A and the rowsof the VCSELs 16A are made to be parallel to each other. In other words,an edge at the side of the upstream of the scanning direction of thelight receiving surface 50A is made to be parallel to the row of theVCSELs 16A. Therefore, as compared to a case in which the longitudinaldirection of the light receiving surface 50A of the photosensor 50 ismade to be parallel to the sub scanning direction, there is a smallerdifference in timings that the plural light beams emitted from theplural VCSELs 16A configuring the SOS detection group enter the lightreceiving surface 50A of the photosensor 50.

Thereby, in the case of lighting the all of the plural VCSELs 16Aconfiguring the SOS detection group, as shown in the graph of FIG. 3,there is a small difference in timings of rising and falling forrespective light beams, and the received light energy profile of whichmaximum value is larger than the light emission energy amount of eachVCSEL 16A is formed on the light receiving surface 50A of thephotosensor 50. As a result, it is possible to have two cross pointsbetween the received light energy profile and the energy levelcorresponding to the threshold for generating the SOS signal withoutraising the amplification gain of the photodiode PD or lowering thethreshold voltage.

Particularly, since the edge at the side of the upstream in the scanningdirection of the light receiving surface 50A is made to be parallel tothe row of the VCSELs 16A, plural light beams emitted from the pluralVCSELs 16A enter the light receiving surface 50A of the photosensor 50at the same time. Thereby, a received light energy profile having risingand falling once, of which maximum value is plural times (for example,three times as shown in the drawing) as the light emission energy amountof each VCSEL is formed.

Accordingly, the stable SOS signal that is not easily affected by thenoise can be generated by the photodetector for SOS signal detection 52,so that the accuracy for the control of the scanning start position inthe main scanning direction at the photoreceptor 46 can be improved.

In addition, as shown in FIG. 1, the reflection surface of the polygonmirror 40 and the light receiving surface 50A of the photosensor 50 arein a conjugate relation by the lens 49 disposed between the polygonmirror 40 and the photosensor 50 and having the positive power in thesub scanning direction. As a result, even if the surface tangle of thereflection surface of the polygon mirror 40 occurs, the incidenceposition of the light beams to the light receiving surface 50A of thephotosensor 50 is not shifted to the sub scanning direction.

In addition, as shown in FIGS. 4A to 4C, the photosensor 50 is supportedby a sensor adjusting mechanism 58 on a bottom surface 10A of a lightscanning device housing so as to be adjusted capable of rotating aroundan optical axis. The sensor adjusting mechanism 58 is configured by apositioning projection 72 that projects from the bottom surface 10A andfaces the lower left side of the photosensor 50, an adjustment screw 73that projects from the bottom surface 10A and faces the lower right sideof the photosensor 50, a plate spring 74 that abuts against the uppersurface of the photosensor such that the photosensor 50 and thepositioning projection 72 and the adjustment screw 73 arepress-contacted, and a supporting mechanism 75 that supports thephotosensor 50 so as to be unable to incline to the optical axialdirection.

The supporting mechanism 75 is configured by a support chip 76 on whicha positioning projection 76A is formed so as to face a center part atthe lower side of the surface of the photosensor 50, a plate spring 77that abuts against the center part at the lower side of the rear surfaceof the photosensor 50 such that the photosensor 50 and the positioningprojection 76A are press-contacted, a supporting chip 78 on which apositioning projection 78A facing the right upper side of the rearsurface of the photosensor 50 is formed, and a supporting chip 79 onwhich a positioning projection 79A facing the left upper side of therear surface of the photosensor 50 is formed.

The photosensor 50 is supported in a sandwich manner by the positioningprojection 76A and the plate spring 77 at the lower center parts. Inaddition, the lower center part of the photosensor 50 is biased from therear side to the front side. When a moment from the front side to therear side acts on the upper side of the photosensor 50, the right upperside of the rear surface and the left upper side of the rear surface ofthe photosensor 50 abut against the positioning projections 78A and 79A,respectively. Thereby, the photosensor 50 cannot be inclined to thelight axial direction.

In addition, the photosensor 50 is supported in a sandwich manner by thepositioning projection 72, the adjustment screw 73, and the platy spring74 at the upper and lower surfaces thereof Here, the adjustment screw 73can adjust the projection amount thereof from the bottom surface 10A andby adjusting the projection amount from the bottom surface 10A of theadjustment screw 73, the light receiving surface 50A of the photosensor50 can be rotatably adjusted around the optical axis. Thereby, it ispossible to suppress shifting of the incidence position of the lightbeam to the light receiving surface 50A of the photosensor 50 that isgenerated by the optical surface tangle of the reflection surface of thepolygon mirror 40 or the like.

Here, as a cause of the positional displacements of the beam spot on thephotoreceptor 46 and the light receiving surface 50A of the photosensor50, an error of interval of the light emission points on the VCSEL array16, an error of properties and an error of attaching positions in thelight scanning device 10 may be conceived.

However, since the VCSEL array 16 is made by a semiconductor process,the error of intervals of the light emission points on the VCSEL array16 is not serious. Further, with respect to the error of properties andthe error of the attaching positions in the light scanning device 10,providing a mechanism for adjusting the attaching position in acondition in which each optical member is appropriately designed andmanufactured, it is possible to obtain a beam spot positionapproximately as calculated although there is a positional displacementto some extent.

Therefore, in a case of generating a SOS signal using only one group (aG1 group) as shown in FIG. 2 as a SOS detection group, an image with asufficient quality can be obtained when the light scanning device 10 isapplied to the image forming device by adding or subtracting a timingcorrection time HT obtained by the following formula (1) to or fromlighting timing of the light beam of the other gropes (here, a G2 groupand a G3 group) that are offset from the SOS detection group in the mainscanning direction so that the beam position offset in design iscorrected with respect to timing derived on the basis of the generatedSOS signal.HT=OD/SS   (1)

Where OD is a beam spot offset distance on the photoreceptor 46 and SSis a beam spot scanning speed on the photoreceptor 46.

FIG. 5 shows the configuration of an exposure control section 90 of thelight scanning device 10 according to the first exemplary embodiment.Here, the VCSELs in the VCSEL array 16 are configured so as tocorrespond to the beam spots shown in FIG. 2, namely, the VCSELs in theVCSEL array 16 are configured in such a manner that three VCSEL groupseach having three VCSELs arranged at approximately even intervals on aline along the sub scanning direction that is perpendicular to the mainscanning direction are arranged, so that the sub scanning directionalposition of each VCSEL is displaced with each other, along the mainscanning direction. Further, assuming that respective VCSEL groups are aGI group, a G2 group, and a G3 group, the SOS signal is generated by thelight beams from the VCSEL group only, which is the G1 group.

As shown in FIG. 5, the exposure control section 90 according to thefirst exemplary embodiment includes a photodetector for SOS signaldetection 52, a video signal output circuit 60, and a VCSEL drivingcircuit 70.

As described above, the photodetector for SOS signal detection 52 isconfigured in the same way as the photodetector shown in FIG. 9.

The video signal output circuit 60 is configured by an oscillator 62, aclock phase synchronous circuit 64, a counter circuit 66, a timingcircuit 68, plural video memories MG 1-1 to MG 3-3, and a SOS detectiongroup lighting control circuit 69. Further, the video memories MG 1-1 toMG 1-3 correspond to respective VCSELs belonging to the G1 group, thevideo memories MG 2-1 to MG 2-3 correspond to respective VCSELsbelonging to the G2 group, and the video memories MG 3-1 to MG 3-3correspond to respective VCSELs belonging to the G3 group.

The SOS detection group lighting control circuit 69 outputs the signals,that can light all VCSELs belonging to SOS detection group (the G1 groupaccording to this exemplary embodiment), to the VCSEL driving circuit 70for a time period that the light beams can be incident to the reflectionmirror 48. Thereby, plural light beams emitted from the VCSELs belongingto the SOS detection group are incident to the photosensor 50 and a SOSsignal (refer to FIG. 6) depending on a light amount level of the plurallight beams is generated by the photodetector for SOS signal detection52.

In addition, in the video signal output circuit 60, the SOS signalgenerated by the photodetector for SOS signal detection 52 and a clocksignal generated by the oscillator 62 are inputted in the clock phasesynchronous circuit 64, and a video clock signal in synchronization withrising timing of the SOS signal is outputted.

To the counter circuit 66, the SOS signal and the video clock signal areinputted, in the counter circuit 66, a number of video clock is countedas the elapsed time from rising of the SOS signal, and a count signalindicating a count value is outputted to the timing circuit 68.

The timing circuit 68 generates an LS1 signal that becomes a high levelwhen a time TO shown in FIG. 6 has passed and becomes a low level aftera predetermined time for allowing reading of video signal shown in FIG.6 passed, on the basis of the count signal inputted from the countercircuit 66, and then, the timing circuit 68 output the signal.

Each of the video memories MG 1-1 to MF 3-3 is structured by a FIFO(First-In First-Out) memory, and, on the basis of the image data, avideo signal for lighting each VCSEL beam that is transformed by a videosignal processor (not illustrated) is stored.

When the LS1 signal becomes the high level, it is inputted in the videomemories MG 1-1 to MG 1-3 corresponding to the respective VCSELs of theG1 group shown in FIG. 2 as a reading allowing signal, video signals SG1-1 to SG 1-3 for the VCSELs belonging to the G1 group are outputtedfrom the video memories MG 1-1 to MG 1-3 in synchronization with thevideo clock signal, and when each video signal is ON, the VCSEL drivingcircuit 70 lights the corresponding VCSELs.

Here, it is necessary to delay the lighting timings of the VCSELsbelonging to the G2 group and the lighting timings of the VCSELsbelonging to the G3 group in FIG. 2, with respect to the lighting timingof the VCSELs belonging to the G1 group, by amounts corresponding to anoffset OF1 and an offset OF2 shown in FIG. 2 respectively.

As shown in FIG. 6, each delay time is obtained from the followingformulas (2) and (3).Delay time T1 of G2 group=OF1/scanning speed   (2)Delay time T2 of G3 group=OF2/scanning speed   (3)

Therefore, in order to expose by the beams of the VCSELs belonging toeach of the G2 group and the G2 group at a predetermined position,outputting a LS2 signal in which the LS1 signal is delayed by the delaytime T1 and a LS3 signal in which the LS1 signal is delayed by the delaytime T2 from the timing circuit 68, each signal is applied as “a videomemory reading allowing signal of a G2 group” and “a video memoryreading allowing signal of a G3 group”.

Then, in the same way as the lighting order of the VCSELs belonging tothe G1 group, the VCSEL corresponding to each video signal is lighted.

The VCSEL array 16 corresponds to the light source in an aspect of theinvention; the VCSEL 16A corresponds to the light emitting element inthe aspect of the invention; the photosensor 50 corresponds to thephotosensor in the aspect of the invention, the photodetector for SOSsignal detection 52 corresponds to the generation section in the aspectof the invention; and the SOS detection group lighting control circuit69 corresponds to the control section in the aspect of the invention.

Further, the explanation of this exemplary embodiment is given assumingthat the SOS detection group is a group which scans the photodetector atthe earliest timing, however, the invention is not limited to this andeven if the SOS detection group is defined as the other group, there isno problem if the timing circuit 68 is appropriately set.

In addition, the explanation of this exemplary embodiment is givenassuming that the video memory reading allowing signal is delayed by thetiming circuit 68 in unit of a video clock signal, however, the presentinvention is not limited to this and the beam spot position of theVCSELs belonging to the G2 group and the G3 group can be controlled witha higher degree of accuracy by providing a fine adjusting mechanismusing delaying by an analog element or a logic gate.

In addition, the explanation of this exemplary embodiment is givenassuming that the correction of the beam position offset with respect tothe G2 group and the G3 group from the G1 group is made in accordancewith a designed value, however, the invention is not limited to this andit is obvious that the invention is made so as to make the correction inaccordance with a measured value.

Second Exemplary Embodiment

According to the first exemplary embodiment, the photosensor 50 isinclined to the downstream side in the main scanning direction withrespect to the sub scanning direction so as to make the light receivingsurface 50A of the photosensor 50 in parallel with the rows of theVCSELs 16A configuring the SOS detection groups. However, according tothis exemplary embodiment, the light beams are incident to the lightreceiving surface 50A of the photosensor 50 after rotating the row ofthe light beams emitted from the VCSELs 16A configuring each SOSdetection group around the optical axis to decrease an inclined anglewith respect to the sub scanning direction.

As shown in FIG. 7, in the light scanning device 100 of this exemplaryembodiment, an anamorphic lens 80 is disposed in place of theabove-described lens 49. As shown in FIGS. 8A to 8C, the anamorphic lens80 is supported on the bottom surface 10A of the light scanning devicehousing so as to be rotatably adjusted around the optical axis by a lensadjusting mechanism 81. The lens adjusting mechanism 81 is configured bya positioning projection 82 that projects from the bottom surface 10Aand faces the lower left side of the anamorphic lens 80, an adjustmentscrew 83 that projects from the bottom surface 10A and faces the lowerright side of the anamorphic lens 80, a plate spring 84 that abutsagainst the upper surface of the anamorphic lens 80 such that theanamorphic lens 80 and the positioning projection 82 and the adjustmentscrew 83 are press-contacted, and a supporting mechanism 85 forsupporting the anamorphic lens 80 so as not to be unable to incline inthe optical axial direction.

The supporting mechanism 85 is configured by a support chip 86 on whicha positioning projection 86A is formed so as to face a center part atthe lower side of the surface of the anamorphic lens 80, a plate spring87 that abuts against the center part at the lower side of the rearsurface of the anamorphic lens 80 such that the anamorphic lens 80 andthe positioning projection 86A are press-contacted, a supporting chip 88on which a positioning projection 88A which faces the right upper sideof the rear surface of the anamorphic lens 80 is formed, and asupporting chip 89 on which a positioning projection 89A which faces theleft upper side of the rear surface of the anamorphic lens 80 is formed.

The anamorphic lens 80 is supported in a sandwich manner by thepositioning projection 86A and the plate spring 87 at the lower centerparts. In addition, the lower center part of the anamorphic lens 80 isbiased from the rear side to the front side. When a moment from thefront side to the rear side acts on the upper side of the anamorphiclens 80, the right upper side of the rear surface and the left upperside of the rear surface of the anamorphic lens 80 abut against thepositioning projections 88A and 89A, respectively. Thereby, theanamorphic lens 80 cannot be inclined to the light axial direction.

In addition, the anamorphic lens 80 is supported in a sandwich manner bythe positioning projection 82, the adjustment screw 83, and the platyspring 84 at the upper and lower surfaces thereof Here, the adjustmentscrew 83 can adjust the projection amount thereof from the bottomsurface 10A and by adjusting the projection amount from the bottomsurface 10A of the adjustment screw 83, the anamorphic lens 80 can berotatably adjusted around the optical axis.

Here, by adjusting the anamorphic lens 80 in a rotating manner, theimaging position of the light beam on the light receiving surface 50A ofthe photosensor 50 is adjusted, however, according to this exemplaryembodiment, after plural light beams emitted from plural VCSELs 16Aconfiguring the SOS detection group pass through the anamorphic lens 80,the inclined angle to the sub scanning direction of the row of the lightbeams is decreased, and further, the row of the light beams is adjustedto be made to be parallel to the longitudinal direction of the lightreceiving surface 50A of the photosensor 50.

Therefore, as compared to a case that the light beams are incident tothe light receiving surface 50A of the photosensor 50 in a state inwhich the row of the light beams emitted from the plural VCSELs 16Aconfiguring the SOS detection group is inclined to the sub scanningdirection, a difference in timings that the plural light beams enter thelight receiving surface 50A of the photosensor 50 is smaller. In themeantime, each member configuring the lens adjusting mechanism 81 isarranged so as not to intercept the light beams progressing to thephotosensor 50 or the photoreceptor 46.

Thereby, when lighting all of the VCSELs 16A configuring the SOSdetection group, as shown in the graph of FIG. 3, a difference intimings of rising and falling of the respective light beams is smallerand the received light energy profile of which maximum value is largerthan the light emission energy of each VCSEL 16A is formed on the lightreceiving surface 50A. As a result, it is possible to have two crosspoints between the received light energy profile and the energy levelcorresponding to the threshold for generating the SOS signal withoutraising the amplification gain of the photodiode PD or lowering thethreshold voltage.

Particularly, since the edge at the side of the upstream in the mainscanning direction of the light receiving surface 50A is made to beparallel to the row of the light beams scaning the light receivingsurface 50A, plural light beams emitted from the plural VCSELs 16A enterthe light receiving surface 50A of the photosensor 50 at the same time.Thereby, a received light energy profile having rising and falling once,of which maximum value is plural times (for example, three times asshown in the drawing) as the light emission energy amount of each VCSELis formed.

Accordingly, the stable SOS signal that is not easily affected by thenoise can be generated by the photodetector for SOS signal detection 52,so that the accuracy for control of the scanning start position in themain scanning direction at the photoreceptor 46 can be improved.

The foregoing description of the exemplary embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theexemplary embodiments were chosen and described in order to best explainthe principles of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

1. A light scanning device comprising: a light source including aplurality of light emitting elements that are arranged linearly; adeflection section that deflects a plurality of light beams emitted fromthe light source to scan a surface to be scanned; a photosensor thatreceives at least one of the plurality of light beams that are deflectedby the deflection section; a signal generation section that generates asignal when an amount of light energy received at the photosensorreaches a predetermined amount; and a control section that startsscanning of the surface to be scanned by each light beam after apredetermined amount of time passes from a point in time when the signalis generated by the signal generation section; wherein a light receivingsurface of the photosensor is inclined so as to receive light beamsemitted from at least two light emitting elements among the plurality oflight emitting elements.
 2. The light scanning device according to claim1, wherein a longitudinal direction of the light receiving surface ofthe photosensor is made to be parallel to a row of the light emittingelements.
 3. The light scanning device according to claim 1, furthercomprising a sensor adjustment section that adjusts an inclined anglewith respect to a sub scanning direction by rotating the photosensoraround an optical axis.
 4. The light scanning device according to claim1, further comprising a lens that has a positive power in a sub scanningdirection and causes a deflection surface of the deflection section andthe light receiving surface to have a conjugate relation.
 5. The lightscanning device according to claim 1, wherein a plurality of rows areformed at the light source, each of the rows having a plurality of lightemitting elements arranged on a line inclined toward one side in a mainscanning direction with respect to a sub scanning direction.
 6. A lightscanning device comprising: a light source including a plurality oflight emitting elements that are arranged linearly; a deflection sectionthat deflects a plurality of light beams emitted from the light sourceto scan a surface to be scanned; a photosensor that receives theplurality of light beams that are deflected by the deflection section;an anamorphic lens disposed between the deflection section and thephotosensor; a lens adjustment section that adjusts incident positionsof the light beams on a light receiving surface of the photosensor byrotating the anamorphic lens around an optical axis; a signal generationsection that generates a signal when an amount of light energy receivedat the photosensor reaches a predetermined amount; and a control sectionthat starts scanning of the surface to be scanned by each light beamafter a predetermined amount of time passes from a point in time whenthe signal is generated by the signal generation section; wherein theanamorphic lens converges the plurality of light beams deflected by thedeflection section in a scanning direction at the light receivingsurface of the photosensor to make the plurality of light beams incidenton the light receiving surface of the photosensor.
 7. The light scanningdevice according to claim 6, wherein a plurality of rows are formed atthe light source, each of the rows having a plurality of light emittingelements arranged on a line inclined toward one side in a main scanningdirection with respect to a sub scanning direction.
 8. The lightscanning device according to claim 7, wherein the lens adjustmentsection rotates the anamorphic lens around the optical axis such that arow of light beams emitted from the plurality of light emitting elementsof the row is made to be parallel to a longitudinal direction of thelight receiving surface of the photosensor.
 9. A light scanning devicecomprising: a light source including a plurality of light emittingelements that are arranged linearly; a deflection section that deflectsa plurality of light beams emitted from the light source to scan asurface to be scanned; a photosensor that receives at least one of theplurality of light beams that are deflected by the deflection section; asignal generation section that generates a signal when an amount oflight energy received at the photosensor reaches a predetermined amount;and a control section that starts scanning of the surface to be scannedby each light beam after a predetermined amount of time passes from apoint in time when the signal is generated by the signal generationsection; wherein a peak of a waveform of the light energy received atthe photosensor is higher than a peak of a waveform of light energyemitted from each of the plurality of light emitting elements of thelight source.
 10. A light scanning device comprising: a light sourceincluding a plurality of light emitting elements that are arrangedlinearly; a deflection section that deflects a plurality of light beamsemitted from the light source to scan a surface to be scanned; aphotosensor that receives at least one of the plurality of light beamsthat are deflected by the deflection section; a signal generationsection that generates a signal when an amount of light energy receivedat the photosensor reaches a predetermined amount; and a control sectionthat starts scanning of the surface to be scanned by each light beamafter a predetermined amount of time passes from a point in time whenthe signal is generated by the signal generation section; wherein a rowof the light emitting elements is inclined toward one side in a scanningdirection on a light receiving surface of the photosensor with respectto a sub scanning direction, and the light receiving surface of thephotosensor is inclined toward the one side in the scanning direction onthe light receiving surface with respect to the sub scanning direction.11. The light scanning device according to claim 10, wherein alongitudinal direction of the light receiving surface of the photosensoris made to be parallel to the row of the light emitting elements. 12.The light scanning device according to claim 10, further comprising asensor adjustment section that adjusts an inclined angle with respect tothe sub scanning direction by rotating the photosensor around an opticalaxis.
 13. The light scanning device according to claim 10 furthercomprising a lens that has a positive power in the sub scanningdirection and causes a deflection surface of the deflection section andthe light receiving surface to have a conjugate relation.